The Underground Environmentalists (Cont.)

When the digging starts we can encounter one of three things:

• Tanks that have been made permanently safe by being filled with a special concrete mix called slurry. This means the tank is heavy to handle, but it is more or less a straightforward excavation. Also, most of the slurry can be used to backfill the hole the tank leaves behind, so there are no disposal problems.
• Tanks that have been made permanently safe by being filled with a foam called RG22. This is much lighter than slurry, but requires special clothing and facemasks to handle, as well as careful disposal.
• The most dangerous situation occurs when the forecourt has only recently closed and there is still some residual petrol/diesel, mixed with sludge at the bottom of the tank, with the rest of the vessel being filled with a mixture of vapour and air.

This last situation needs very special care, as a mixture of petrol vapour and air in an enclosed metal vessel can legitimately be called a bomb.

As all nuts and bolts, cutters, spanners and other tools are made of steel, there is always a danger of creating a spark and setting off an explosion, but this risk can be eliminated by pumping water or nitrogen foam into the tanks, which pushes the air and petrol vapour out. We then either let the nitrogen bubbles burst, ventilate the tank and remove the remaining liquid, or, in the case of water filled tanks, pump the water and residual product out through a portable cleaning machine, which separates the water from the sludge. Water will go down the foul sewer and residual product is disposed of properly off-site.

Some companies jet wash from the surface, which creates more contaminated water than necessary – which then has to be disposed of – and, we believe, does not get the tank sufficiently clean.  Our procedure, as with some other specialists, is to completely uncover the tank and cold–cut a large hole in the top of the tank, so that one of our operatives can go into the tank – wearing full protective clothing and breathing apparatus – and scrub it thoroughly by hand.

We, and many of our clients, believe it is important to thoroughly clean any tanks and fuel lines that are going to be scrapped, as the metal from these goes to smelters and general scrap yards, where the workforce only wear basic protection, such as gloves, and are not set up for dealing with contaminant. Contaminated material should only go to specialist sites. Therefore, it is our duty to ensure that everything that leaves the site is as safe as possible and we believe that this can only be done by getting inside the tank and scrubbing.

As well as excavating the tanks we also dig test pits where our environmental consultants indicate there may be pollution.

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